Circuit breaker



Aug. 11, 1936. H. J. CRABBS ET AL 2,050,277

CIRCUIT BREAKER Filed Aug. 15, 19:54

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ATTORN Patented Aug. 11, 1936 UNITED STATES PATENT OFFICE CIRCUITBREAKER Herbert J. Crabbs and Herbert L. Rawlins, Wilkinsburg, Pa.,assignors to Westinghouse Electric & Manufacturing Company, EastPittsburgh, Pa., a corporation of Pennsylvania Application August 15,1934, Serial No. 739,892

Claims.v (Cl. 200117) These devices take a multitude of forms, but

perhaps the best known, and certainly the most widely used, is theso-called expulsion fuse. Expulsion fuses fulfill a very definitemission in the 10 electric art, in that they constitute a means wherebyprotection, against abnormal circuit conditions, may be given toelectrical apparatus at a very low cost. Their application is limitedonly because of the fact that they are inherently one operation device,and must be serviced after each operation.

During the circuit interrupting operation, the heat of the are which isestablished by the melting of the fusible link causes the evolution oflarge quantities of gas from the walls of the main fuse tube, and thisgas, in venting, flows expulsively through the are, thereby effectingits extinguishment. The device is restored to an operative conditionfollowing each operation by replacing 5 the used fusible 'unit with anew one.

One of the most successful commercial forms of expulsion fuse devicescomprises a tube, of fiber or other material which is capable ofevolving arc extinguishing gas when placed in prox- 30 imity to anelectric arc, conducting terminal members mounted at the ends of thetube, and a replaceable fusible unit disposed within the tube forconnecting the terminals and for opening the electrical circuittherethrough upon the oo- 35 currence of predetermined overloadconditions. One end of the tube isnormally closed and the other end isnormally open. Upon the occur- 7 rence of an overload or other abnormalcondition the fusible element melts and an arc is estab- 40 llshedwithin the fuse tube.

In the ordinary operation of these devices, they are called upon tointerrupt overloads of widely varying magnitude, and, since thedimensions of the main tube must be sufficiently large to ac- 45conimodate the largest magnitude are which may be established therein,some difiiculty has been experienced with the prior art devices in theinterruption of low-current overloads. This dimculty has arisen becauseof the fact that the arcs 50 which are produced by low-magnitudeoverloads are of comparatively small cross sectional area, and thus donot 'cohtacitthe gas evolving walls of the'inain tube sufficientlyintimately to produce an adequate amount of arc extinguishing Thedifficulty of satisfactorily interrupting lowcurrent magnitude arcs isfurther aggravated, where a simple link-type fusible unit is usedbecause of the fact that only a small portion of the fusible element ismelted by the overload, 5 and, since little gas is evolved, theremaining conducting portions of the fusible means are not expelled fromthe tube so as to draw a long are. The result is that on low currentoverloads only a short are is drawn and little gas is produced for 10isfactory than the older devices. Upon the occurrence of large magnitudeoverloads, the operation is substantially the same as for the unbiasedunits. The heavy-magnitude overloads cause a 20 substantiallyinstantaneous fusion of the fusible element with a resultant largeevolution of gas in the walls of the fuse tube and the combined re sultis to expel the entire fuse means from the tube, thereby securing a longarc which is quickly extinguished by the out-flowing blast of gas. Whenthe device is interrupting low-magnitude overloads, the action of thebiasing springs is such as to secure a long arc immediately followingthe fusion of the fusible element, and the devices are so proportionedthat this are is too long to be self-sustained whether or not the gasevolution is very large.

As a further improvement for very low-current operation, an auxiliarytube of insulating material having a cross-sectional area considerablyless than that of the main tube is disposed about the fusible elementproper. The walls of this tube are relatively weak and are practicallyimmediately ruptured when a large-current-mag-p 40 nitude is drawn, butare capable of aiding very. considerably in the extinction ofsmall-magnitude arcs by the provision of a suitably directed stream ofarc extinguishing gas.

Certain difficulties have arisen in the utilization of spring biasedfusible elements. Most of these devices have utilized a single tensionspring which is stressed when the renewable fuse unit is installedwithin the main tube of the interrupter. Due to difference in thedimensions of the tubes and in the manner of servicing the devices, theamount of stress on the spring is a variable quantity and thecalibration of the fusible element is thus rendered more or lessuncertain. It would appear that the solution of this problem liesin whenit is intended that that device should be used as refill units for fusestructures nowin existence. Different electrical manufacturers haveutilized different sized terminals, tubes, and the like for theirexpulsion fuses. Practically all ex isting power systems utilize anumber of different fuse structures, and to simplify the problem ofmaintenance and to reduce the cost of the stocks of replacement fuseswhich must be carried, it is highly desirable that the refill fuse unitbe provided with suitable means for allowing the device to be utilizedin any of the existing structures.

The principal object of our invention, therefore, is to provide animproved, universally applicable replacement fuse structure which shallbe suitable for use in all existing types of expulsion fuse devices, andwhich shall be superior in its operating characteristics to thepreviously known devices.

Another object of our invention is to provide an improved fuse unit forexpulsion fuses or simi- 'lar devices which shall be provided with twospring biased fusible element wherein the biasing force exerted by thespring on the fusible section is accurately adjusted to a fixed valueduring the manufacture of the fuse, in order to secure the maximumpossible accuracy of calibration of the device.

A second further object of our invention is to provide a spring biasedfusible element which shall utilize a compression spring for supplying atensioning force to the fusible section of the element.

A still further object of our invention is to provide an improvedterminal means for use with electric fuses generally, our improved meansto permit a single fuse refill unit to be used with structures havingfuse engaging means of differing dimensions, our improved terminal meansto utilize no loose parts which might become lost and to be so arrangedthat a good electrical connection is assured at all times. I

These and other objects of our invention will be made more apparent fromthe following description of a preferred embodiment of our invention.Referring to the drawing:

Figure 1 is a sectional view, partially in elevation, of an expulsionfuse utilizing a refill unit which includes the principal features ofour invention.

Fig. 2 is an enlarged sectional view, partially in elevation, of therefill unit forming a part of the fuse structure shown in Fig. 1.

Fig. 3 is a fragmentary elevation view showing the fusible sections ofthe refill unit illustrated in Fig. 2.

Fig. 4 is a developed plan view of the upper terminal of the refill unitshown in the other figures of the drawing.

Fig. 5 is an enlarged sectional view on the line V-V of Fig. 2.

- Fig. 6 is a fragmentary perspective view of the upper terminal portionof the refill element shown in Figs. 1 and 2, and

Fig. 7 is a developed plan view of a modified upper terminal membersuitable for use with the refill unit illustrated in the other figuresof the drawing.

The expulsion fuse structure which is shown in Fig. 1 includes a maintube ll of fiber or other suitable insulating material, which isthreaded at its unit it in contact with the upper contact member 5. Therefill unit itself is positioned within the main fuse tube l and isprovided with a flexible conductor is for engaging the screw connection[15 which forms a part of the lower ferrule 3 in order to complete theelectrical circuit through the device. The lower end of the fuse tube lis normally open in order to allow a free out-flow of the gas which isevolved from the walls of the main tube. during the circuit interruptingoperation.

In order to obtain the greatest possible extension ofthe'operating rangeof the fuse, the refill unit is provided with two serially connectedfusible elements, each of which will be described in some detail later.One of these elements is adapted to fuse substantially instantaneouslyupon the occurrence of heavy overloads or other similar circuitdisturbances, and the other element is adapted to fuse after a timedelay upon the occurrence of prolonged moderate overloads. Thisarrangement, while giving adequate protection to the connectedequipment,serves to minimize undesirable and annoying discontinuities in the flowof power throughthe system.

The upper terminal portion ll of the refill element 9, as is shownparticularly in Figs. 2 and 4, comprises a fiat sheet of conductingmaterial which is cut so as to form a plurality of cooperating circularsections l1, l8, l9 and 2|, which may be bent one over the other so asto define button or cap-type terminals of at least two differentdimensions. The method of bendin this terminal portion H is shownparticularly in Fig. 6, wherein the several elements have been bent toform the largest possible button or cap-type terminal for the refillelement. If a cap portion having a smaller diameter is desired, thelarger of the cooperating sections ll of the upper terminal member I Iis bent back and forth a few times so as to cause it to be broken awayfrom the remaining sections, thus leavinga. cap having the diameter ofthe section Hi. If it is desired to use the device in a device must becapable of accommodating itself to other structures.

By forming the entire terminal portion II from a single sheet ofconducting material, all loose parts are eliminated, and one serious0bjection to some of the prior art devices isovercome. Also, thisarrangement assures a good electrical connection between the refillterminal and the refill itself, thus preventing high resistance contactsand their accompanying dangers.

The lower end of the shank portion 23 of the upper terminal member II issomewhat narrower than the main body of that portion and is adapted toextend into suitable slots 29 pro vided in the upper end of an auxiliaryfuse tube 21 which forms apart of the refill unit. The lower edges 3| ofthe body portion 23 serve as shoulders for engaging the ends of theslots 29. 1

Two holes 33 are punched in the reduced section of the body portion 23for allowing the pasing the manufacture of the refill unit to anydesired value, for producing a tensioning force upon both of the fusibleelements of the refill unit.

The resistance of .the member 45 is so proportioned that the heatingproduced by the prolonged flow therethrough of a predetermined currentis capable of effecting the melting of the low melting point solderwhich serves to connect that member with the upper fusible element 31and the terminal portion 41. When this occurs the biasing action of thespring 5| effects the opening of the electrical circuit through therefill unit at that point. The accurate tensioning 0f the fusibleelements which is made possible by the utilization of a compressionspring which is adjusted at the factory, assures accurate calibrationand accurate maintaining of the calibration of both of the fusibleelements.

sage of two rivets 35 which are adapted to electrically and mechanicallyconnect the upper terminal 39 of the instantaneousfusible element 31thereto. This fusible element 31 comprises a fiat strip of conductingmaterial which, in addition to the enlarged terminal portion 39 forengaging the lower end of the upper terminal member, is provided with aportion 4| of reduced cross-sectional area, which is adapted to fusesubstantially instantaneously upon the passage therethrough ofpredetermined magnitude currents, and a lower portion 43 which isadapted to be soldered by a low melting point solder to aflat.conducting member 45 of substantially the same cross sectionaldimensions as the lower portion of the fusible element itself.

The member 45 is formed of a resistance material such as German silveror the like, and is soldered at its lower end, likewise by a low meltingpoint solder, to a terminal strip 41, the lower end of which, in turn,is soldered by a high melting point solder to the upper end of theflexible conductor 3. The member 45 and the two associated solderedjoints comprise the second fusible element.

The auxiliary fuse tube 21 is of suflicient length to enclosethe-fusible portion 4| of the upper fusible element 31 and the twosoldered connections'of the member 45 positioned beneath that element.At its lower end, the auxiliary fuse tube 21 is provided with a hollowcylindrical member 49, which may be of metal, for positioning the upperend of the compression spring 5|, the upper end of this spring beingadapted to abut against the lower end of the auxiliary fuse tube 21 whenthe device is in the normal operative position. The lower end of thecompression spring 5| engages a suitable funnel shaped member 53 whichis rigidly soldered to the flexible conductor, in the position shown inFig. 2, during the assembling of the device.

As mentioned previously, the shoulders 3| which form a part of the upperterminal member engage the lower ends of the slots 29 cut in theauxiliary fuse tube 21, and serve to-trans mit the reaction force of thecompression spring 5| to the upper end of the upper fusible'portion 4|of the refill element. The biasing force of the 7 Upon the occurrence ofa very heavy overload in the controlled circuit, the upper fusibleelement is melted at the portion 4|, substantially instantaneously, andthe compression spring 5| is then free to move all of the conductingportions of the refill unit disposed beneath'the upper fusible portionout of the auxiliary fuse tube 21. The are drawing operation, followingthe occurrence of very heavy overload takes place, however, at extremelyhigh speed, and simultaneously with the separation of the terminalportions 39 and 43 of the upper fusible element, which is effected bythe biasing spring 5|, there is a large evolution of the gas from theauxiliary fuse tube 21 which may effect a rupture of the tubeaccompanied by an expanding of the are into the main fuse tube If theare energy is very large, the rate of gas evolution soon becomessufficient to effect a very rapid expelling of the auxiliary fuse tube29, the

spring 5|, and the flexible conducting member l3 from the lower open endof the main tube with the result that a long arc is establishedtherewithin. This are contacts the walls of the tube and evolves a veryconsiderable quantity of arc extinguishing gas which gas in ventingflows expulsively through the open lower end of the fuse tube, therebyeffecting the extinguishment of the arc.

Upon the occurrence of ,a low magnitude overload, the resistance member45 begins to heat, and if the overload persists for a sufficient periodof time the heating causes the low melting point solder to be melted.Simultaneously with the melting of this solder the compression spring 5|moves the flexible lead l3 and the .terminal strip 41 aflixed thereto inthe direction of the lower,

fusing of either fusible element usualy produces sufficient reactionforces to cause the spring, the

flexible lead |3, and the terminal 41 aflixed thereto to be movedentirely out of the main fuse tube Even if this is not done, however,there is a sufficient separation of the current-carrying parts to assurea rapid extinction of low magnitude arcs.

The cross-sectional dimensions of the fusible elements are such thatthey may be moved into the central opening within the spring-5| when thespring expands during the operation of the device. This assures thatthere will be no jamming or failure of the device to operate. Thepresence of the auxiliary fuse tube during the interruption of lowmagnitude overloads is of particular value in assuring that the arcshall be subjected to an adequate blast of arc extinguishing gas.

The modified upper terminal member 6 l l which is illustrated in Fig. 7is essentially similar to the previously described member 8 l. Similarto that member, it comprises a flat sheet of conducting material whichis cut so as to define a. plurality of cooperating circular sectionsill, M8, M9, arc and Hill, which may be bent one over the other so astodefine a button or cap-type terminal of at least two differentdimensions. The chief diiierences between the two members reside in theprovision of two shank portions 023 in the modified structure and in thearrangement of the circular sections.

From the foregoing it will be seen that we have provided an improvedrefill unit for use with expulsion fuses or similar devices whichpossess numerous advantages over the devices previously known to theart. Our improved reiill unit is provided with a novel terminal meansfor permitting it to be used with devices whose physical dimensions varyover a considerable range. Moreover, it includes two serially connectedfuelble elements each of which is capable of fusing upon the occurrenceof differing predetermined conditions, and a single compression springfor submitting those elements to a substantially constant tensionlngforce at all times. Further, we have shown how the features of ourimproved refill unit may be embodied into a device which utilizes anauxiliary fuse tube for aiding in the extinction of low magnitudeoverloads.

While in accordance with the patent statutes, we have disclosed theforegoing details of a preferred embodiment of our invention, it is tobe understood that many of thesedetails are merely illustrative, andthat variations in their precise form may be possible and necessary inmany applications. It is our desire, therefore, that the language of theaccompanying claims shall be accorded the broadest reasonableconstruction, and that our invention shall be limited only by what isexpressly stated therein and by the prior art.

We claim the following as our invention:

1. A replacement fuse means, comprising a fusible element, terminalmeans for said element, and a compression spring, which is stressedduring the manufacture of said means, for subjecting said fusibleelement to a substantially constant tension stress at all times, one ofsaid terminal means comprising a liat sheet of metal which is cut so asto provide a plurality of cooperating. sections which may be bent so asto form button terminals of at least two difierent sizes.

2. A replacement fuse unit comprising a fusible element, terminal meanselectrically and mechan= ically connected to either end or said element,one of said terminal members comprising a fiat sheet of conductingmaterial which is cut so as to form a body portion having shouldermembers formed integral therewith and a plurality of cooperatingsections which may be bent so as to form button terminals of at leasttwo different sizes, an auxiliary fuse tube disposed so as to enclosesaid fusible element, and a normally stressed compression spring forsubjecting said fusible element to a substantially constant tensionstress at I all times, one end or said stressed spring beingmechanically connected to the other of said ter minal members, and theother end of said spring abutting against one end of said tube, theother end of said tube engaging said shoulder portions in order totransmit the reaction force of said spring to said first mentionedterminal member.

3. A terminal means for a fusible element comprising a flat sheet ofmetal which is cut so as to form a plurality of cooperating sectionswhich may be bent so as to form terminals of at least two diiierentdimensions.

4. A terminal member for an electric fuse com-- prising a hat sheet ofconducting material having cuts therein forming a plurality ofcooperating circular sections which may be selectively bent so as toform circular terminal members or at least two different diameters.

5. A terminal member for an electric fuse comprising a flat sheet ofconducting material having a shank portion and a plurality ofcooperating sections which may be bent so as to form button terminals ofat least two different dimensions, the axis or" said shank portion beingsubstantially perpendicular to the plane of said button terminal means.

6. A terminal member for an electric fuse comprising a fiat sheet ofconducting material having a body portion of less width than length anda plurality of cooperating circular sections which may be selectivelybent so as to form circular, button type terminals of at least twodifferent diameters, the longitudinal axis of said body portion beingsubstantially perpendicular to the plane of said button terminal means.

7. A terminal means for a fusible element comprising a plurality ofintegrally formed, cooperating portions which define a button head ofpredetermined transverse dimensions, and means whereby at least one ofsaid portions may be readily broken away to effect a change in thetransverse dimensions of said button head.

8. A terminal means for an electric fuse comprising a shank, a pluralityof integrally formed, cooperating portions which define a button head ofpredetermined transverse dimensions at one end of said shank, and meanswhereby at least one of said cooperating portions may be readily brokenaway to effect a reduction in the transverse dimensions of said buttonhead.

9. A terminal member for an electric fuse comprising a fiat sheet ofmetal, cut so as to. form a plurality of integral cooperating sectionswhich may be bent to form a button head of predetermined transversedimensions, and means whereby at least one of said sections may bereadily broken away from said sheet to efiect a change in the transversedimensions of said button head.

10. A terminal member for an electric fuse comprising a fiat sheet ofmetal, cut so as to define a plurality of integral portions which 00-operate to form a shank and a' button head of preetermined transversedimensions amxed to said shank, the longitudinal axis of said shankbeing substantially perpendicular to the plane of said i button head,and means whereby at least one of 5 said portions may be broken awayfrom said sheet to reduce the transverse dimensions of said button head.

' HERBERT J. CRABBS.

HERBERT'L, RAWLINS.

